1. Technical Field
The invention relates generally to a method of predicting an individual's predisposition to QT prolongation, and more particularly, to a method of predicting such predisposition based on a sequence of the individual's ABCC2 (ATP-binding cassette, sub-family C, member 2) gene.
2. Background
Prolongation of the electrocardiographic QT interval (the time between the start of the Q wave and the end of the T wave) is referred to as long QT syndrome (LQTS). LQTS may comprise a genetic component. In some patients with LQTS, QT prolongation can be a chronic condition. In some persons, LQTS may be induced by the administration of an active pharmaceutical ingredient that prolongs the QT interval. A number of compounds are believed to be capable of prolonging the QT interval. These include amiodarone, arsenic trioxide, bepridil, chloroquine, chlorpromazine, cisapride, clarithromycin, disopyramide, dofetilide, domperidone, droperidol, erythromycin, halofantrine, haloperidol, ibutilide, iloperidone, levomethadyl, mesoridazine, methadone, pentamidine, pimozide, procainamide, quinidine, sotalol, sparfloxacin, and thioridazine.
Other compounds are suspected of being capable of prolonging the QT interval, although such prolongation has not been definitively established. These include alfuzosin, amantadine, azithromycin, chloral hydrate, clozapine, dolasetron, felbamate, flecainide, foscarnet, fosphenytoin, gatifloxacin, gemifloxacin, granisetron, indapamide, isradipine, levofloxacin, lithium, moexipril, moxifloxacin, nicardipine, octreotide, ofloxacin, ondansetron, quetiapine, ranolazine, risperidone, roxithromycin, tacrolimus, tamoxifen, telithromycin, tizanidine, vardenafil, venlafaxine, voriconazole, and ziprasidone.
Individuals at risk of suffering LQTS are advised not to use still other compounds, due to the possibility that they may prolong the QT interval. These include albuterol, amitriptyline, amoxapine, amphetamine, dextroamphetamine, atomoxetine, chloroquine, ciprofloxacin, citalopram, clomipramine, cocaine, desipramine, dexmethylphenidate, dobutamine, dopamine, doxepin, ephedrine, epinephrine, fenfluramine, fluconazole, fluoxetine, galantamine, imipramine, isoproterenol, itraconazole, ketoconazole, levalbuterol, metaproterenol, methylphenidate, mexiletine, midodrine, norepinephrine, nortriptyline, paroxetine, phentermine, phenylephrine, phenylpropanolamine, protriptyline, pseudoephedrine, ritodrine, salmeterol, sertraline, sibutramine, solifenacin, terbutaline, tolterodine, trimethoprim-sulfa, and trimipramine.
By fluorescence in situ hybridization (FISH), Taniguchi et al. and van Kuijck et al. mapped the human MRP2/CMOAT gene to 10q24. Taniguchi et al., A human canalicular multispecific organic anion transporter (cMOAT) gene is overexpressed in cisplatin-resistant human cancer cell lines with decreased drug accumulation, Cancer Res. 56: 4124-4129, 1996. PubMed ID: 8797578; van Kuijck et al., Assignment of the canalicular multispecific organic anion transporter gene (CMOAT) to human chromosome 10q24 and mouse chromosome 19D2 by fluorescent in situ hybridization, Cytogenet. Cell Genet. 77: 285-287, 1997. PubMed ID: 9284939. Toh et al. determined the exon/intron structure of the human MRP2/CMOAT gene. They found that the human gene contains 32 exons and spans 200 kb or more genomic DNA. Toh et al., Genomic structure of the canalicular multispecific organic anion-transporter gene (MRP2/cMOAT) and mutations in the ATP-binding-cassette region in Dubin-Johnson syndrome, Am. J. Hum. Genet. 64: 739-746, 1999. PubMed ID: 10053008.
Evers et al., who referred to cMOAT as multidrug resistance-associated protein-2 (MRP2), studied its drug export activity in polarized kidney in MDCK cells. In contrast to MRP1, cMOAT was found predominantly intracellularly in nonpolarized cells, suggesting the cMOAT requires a polarized cell for plasma membrane routing. They found that when kidney epithelial MDCK cells were grown in a monolayer, cMOAT localized to the apical plasma membrane. Their studies demonstrated that cMOAT causes transport of organic anions, including a substrate not shown to be transported by organic anion transporters previously. Transport was inhibited only inefficiently by compounds known to block MRP1. They also showed that cMOAT caused transport of the anticancer drug vinblastine to the apical side of a cell monolayer. They concluded that cMOAT is a 5-prime-adenosine triphosphate binding cassette transporter that may be involved in drug resistance in mammalian cells. Evers et al., Drug export activity of the human canalicular multispecific organic anion transporter in polarized kidney MDCK cells expressing cMOAT (MRP2) cDNA, J. Clin. Invest. 101: 1310-1319, 1998. PubMed ID: 9525973.